Abstract 3493: Epidemiology and Genetic Cause of Sudden Unexplained Nocturnal Death Syndrome in Southern China
Sudden unexplained nocturnal death syndrome (SUNDS) is a sleep disorder that leads to sudden cardiac death in Southeast Asian ethnic groups such as Thai, Japanese, Philippine and Cambodian. SUNDS mainly occurs during sleep in young healthy males without sign of cardiac dysfunction. The lack of epidemiologic data is always being a formidable bottleneck for studying SUNDS around the world. Although the annual occurrence rate of SUNDs is high (over 2/100,000) for the aged 20 to 40 years males in Southern China, the disease epidemiology in regions of China may be underestimated in the absence of systemic monitoring. Autopsy data collected in Guangdong Province (a Southern China province) from 2001–2006 reported 975 cases of SUNDS. Among the victims, 93.2% were males while 6.8% were females. In 772 cases with complete medical records, 86.3% deaths occurred between ages 16 to 40. The peak months for SUNDS occurrence were April (111 cases), May (112 cases) and June (80 cases), which corresponded to highest numbers of fever patients in this period indicating that fever may play a role in SUNDS. In 75.4% cases where witnesses were present, victims died in sleep between 11 PM to 4 AM and showed signs that matched reported cases in other Southeast Asian populations. Other collected data included birthplace and profession and details of events at death. The genetic cause of Chinese SUNDS is being investigated more recently. Mutations in the voltage-gated sodium channel (SCN5A) have been linked to SUNDS. We traced four generations in two families with SUNDS history and in each case, diseased male victims in the second and third generations at the age of 17–38 were found. Surviving relatives did not show any significant cardiac structural defects but their ECGs displayed an abnormal Q wave or sinus bradycardia in male siblings who approached age 30. Mutation screening in the SCN5A gene using specimen obtained from diseased victims and survived relatives was undertaken to identify SUNDS-related mutations in these two families. This is the first report of SUNDS epidemiology and its impact in the Han population of Southern China.